An arrhythmia is a disturbance in the normal rate, rhythm or conduction of the heartbeat. A ventricular arrhythmia originates in the ventricles. Ventricular tachycardia (VT), one form of ventricular arrhythmia, is a condition in which the ventricles contract at a high rate, e.g., 110 or more beats per minute. Ventricular fibrillation (VF), another form of ventricular arrhythmia, is characterized by a chaotic and turbulent activation of ventricular wall tissue. The number of depolarizations per minute during VF can exceed 400.
VT can lead to VF, which in turn can be life threatening. VT is also associated with other low cardiac output symptoms, such as fatigue. Many VTs are episodic, marked by abrupt onset but also abrupt termination, but cause considerable patient distress. If untreated, VT can lead to other dangerous life-threatening conditions, such as the development of blood clots, which can cause stroke and possibly death.
Treatment for tachycardia may include anti-tachycardia pacing (ATP) or cardioversion, in which a train of high rate pulses of one or more high energy pulses is delivered to the heart in an attempt to restore a more normal rhythm. ATP is typically effective in converting stable atrial tachycardias to normal rhythm, and is often delivered via an implanted device. In many cases, a sequence of increasingly aggressive ATP therapies are applied until the VT episode is terminated. The implanted device can be configured to discontinue ATP and immediately apply cardioversion in the event the VT degrades into VF.